1. Field of the Invention
The present invention relates generally to an electrophotographic roller, such as a developer roller including a resistive layer over a semi-conductive core. The roller incorporates organic salts to improve electrical surface resistance and/or overall printing performance, such as resistance to printing defects caused by nip banding.
2. Description of the Related Art
During the image forming process, image forming material, such as toner, may be transferred from toner carrying members (rollers) to print or copy media. For example, a developer roller, which transfers toner to a photoconductive (PC) surface, may be configured with a surface layer of relatively high electrical resistance over a semi-conductive core, which may then provide improved toner transfer and print performance. Such a surface layer may specifically be the result of forming a roller with a diene type polymer (e.g. polybutadiene) in the presence of an inorganic salt and heating/baking in the presence of oxygen to provide an oxidized surface layer. A resistive layer may be formed in this manner having a thickness of about 100 microns from the surface.
With the ever increasing market demands for faster print speeds and improved print quality, the above referenced rollers containing an oxidized surface have nonetheless led to the development of various other printing problems. For example, a typical developer roller may form a nip with a doctor blade and/or a toner adder roller and/or photoconductive drum and/or with a particular cartridge sealing location. Over time, this may lead to what is termed “nip banding”, the practical effect of which is the formation of relatively dark regions on the printed media. Such nip banding also may adversely influence roller electrical properties and therefore may decrease the life of a given printer cartridge. Such nip banding may also be particularly problematic when a printer cartridge experiences a change from a relatively high humidity environment (e.g. greater than 78° F./80% relative humidity) to a relatively low humidity environment (e.g., less than or equal to 60° F./8.0% relative humidity).